As this kind of paper feeding apparatus, there has been known one in which the lowermost one of multiple pasteboards placed in a stacked manner with the leading ends in contact with a reference plane of a guide plate that is provided over a paper feeding table with a clearance gap therebetween is sucked by a suction unit provided under the paper feeding table and, at the same time, fed by a paper feed roll with a portion of a peripheral surface thereof exposed through the paper feeding table intermittently one by one through the clearance gap of the guide plate toward a next-process device shown in Japanese Patent No. 2726516. The paper feed roll then includes ones provided at the stage prior to the guide plate (on the side with the pasteboards placed in a stacked manner) and respectively controlled by a single motor.
In this paper feeding apparatus, to feed the lowermost pasteboard sucked by the suction unit toward the next-process device, upper and lower feed rolls are provided at the stage subsequent to the guide plate (on the next-process device side) for feeding the pasteboard, which is fed by the paper feed rolls into the stage subsequent to the guide plate, through between the nips toward the next-process device. The paper feed rolls then undergo timing control during one cycle until the completion of feeding of the lowermost pasteboard in response to a timing signal from the next-process device.
Incidentally, in such a conventional paper feeding apparatus as described above in which multiple paper feed rolls are respectively controlled by a single motor, the motor is required to be accelerated rapidly from a stopped state to a high rotational speed and then braked rapidly to be stopped during one cycle until the completion of feeding of the lowermost pasteboard. In this case, if the rate of feeding of the pasteboard by the paper feed rolls is increased (e.g., the rate of feeding of the pasteboard with a length of 1100 mm in the feeding direction is 300 sheets/min or higher), the motor cannot be controlled without delay. This is because an operating time (e.g. 100 msec) is required for both of a clutch for power-on/off between the motor and each paper feed roll and a brake for braking each paper feed roll after disengagement of the clutch. Accordingly, since the time required for feeding of the lowermost pasteboard is as short as 200 msec at a rate of feeding of 300 sheets/min or higher, it is obviously and physically impossible to accelerate the motor rapidly from a state where the lowermost pasteboard is stopped to a high rotational speed and then stop it rapidly within the remaining 100 msec, which is a result of subtraction of the operating time for the clutch and the brake.
In view of this, it is conceivable that the paper feed rolls might be configured to be movable up and down through, for example, driving of a link mechanism, driven constantly at their respective highest rotational speeds, and brought into contact/non-contact with the lowermost pasteboard through an up-and-down movement of the link mechanism during one cycle until the completion of feeding of the pasteboard to increase the rate of feeding of the pasteboard by the paper feed rolls.
However, since the paper feed rolls are arranged at regular intervals in the direction of feeding of the lowermost pasteboard, the amount of feeding of the pasteboard is different for each of the paper feed rolls. This requires the paper feed rolls in the direction of feeding of the pasteboard to move independently up and down, resulting in a very complex structure.
The present invention has been made under these circumstances, and an object thereof is to provide a paper feeding apparatus that does not employ clutch and brake-based motor control to increase the rate of feeding of a pasteboard toward a next-process device with a simple structure even without an independent up-and-down movement of each paper feed roll.